The objective of this proposal is to study the molecular mechanism of necroptosis, a cellular necrotic cell death pathway. Apoptosis has been established as a cellular mechanism that regulates programmed cell death. However, it has become increasingly clear that apoptosis is not the only cellular mechanism that regulates cell death. Apoptosis triggered by the activation of death receptors represents a prototypic apoptosis pathway. Interestingly, stimulation of certain apoptotic deficient cells with death receptor ligands such as FasL or TNF[unreadable] has been shown to lead to necrotic cell death termed necroptosis. Cell death with necrotic features (necrosis) is prevalent in cancers, viral infections and other acute pathologies. Furthermore, excessive necrosis in cancers has long been noted as a indicator for poor prognosis. However, very little attention has been directed towards studying necrosis because necrosis is believed to be an unregulated process caused by overwhelming external stress. The discovery of necroptosis offers the possibility that a subset of pathologic necrotic cell death is regulated by a distinct cellular mechanism, and therefore is amenable to therapeutic intervention. A genome-wide siRNA screen of 16,873 genes was carried out to identify genes involved in regulating necroptosis. A set of genes was identified as common mediators of necroptosis that are downstream of RIP1, an essential kinase for the activation of necroptosis. This screen identified a tumor suppressor network previously known to regulate DNA damage response and a BH3-only member of Bcl-2 family in the signaling of necroptosis. This proposal is to characterize the role of necroptosis and RIPI kinase in DFJA damage induced cell death and to determine the mechanism by which RIPI mediates the activation of BH3-only Bcl-2 family member in the execution of necroptosis. This study will provide important molecular insights into a cellular necrotic cell death pathway. Understanding the mechanism by which cells regulate necroptotic cell death may provide unique opportunities for developing novel therapies of major human diseases with little or no known treatment.